SCALES OF INFLUENCE: EVENTS THAT CREATE LAKE SEDIMENT RECORDS

Lake records have long been used to infer climate changes through a wide variety of proxy indicators archived in the sediments. But watershed processes, which operate across many different spatial scales, tend to smooth and lengthen the distribution of sedimentary deposits related to individual events. Even very large events, such as hurricanes, can be masked by mixing of “event sediments” with earlier deposits. For the New England region, model predictions of modern and near future climate change anticipate increased frequency and intensity of short-duration precipitation events. We wonder, can a change in the frequency of high-intensity precipitation events be detected in lake sediment records and, if so, which proxy best documents that change?

This project aims to address these questions and to better understand the magnitude of precipitation needed to create distinct and recognizable deposits in lakes. In the fall of 2017, a short (60 cm) gravity-corer was used to collect near-surface sediments from Norway Pond, Hancock and Pleasant Lake, Deerfield, in south-central New Hampshire. The cores include the sediment-water interface, and are expected to contain at least 200 years of record. The subsamples were analyzed for several physical and chemical properties, including Pb210 ages, carbon content, particle-size, frequency-dependent magnetic susceptibility and mineral geochemistry.

These data will help identify sedimentary properties that correspond to episodes of regional flooding, including two particularly high magnitude events for New Hampshire, Tropical Storm Irene, in 2011, and the Hurricane of 1938. The different sampling resolutions in side-by-side cores will provide added insight into the duration and magnitude of sedimentary responses to particular events. Through the use of physical and chemical analysis we are expecting to determine if short-duration precipitation events mask the sediment signatures of much larger storm events.